This invention relates to a process for removing pollutants from an aqueous stream using a composite which is a mixture of a microporous cation exchange composition and an anion exchange composition. Cation exchange compositions are zirconium metallates and titanium metallates, while examples of anion exchange compositions are hydrous zirconium oxide, zirconia, etc.
It is well known that ammonia or ammonium cation is a serious pollutant in water. At high concentrations ammonium ions are toxic to aquatic life. Ammonium ions in stream, lakes, etc. are converted to nitrites which are also toxic to aquatic life and finally the nitrites are converted to nitrates which are not as toxic as ammonium ions or nitrites, but can contribute to eutrophication. Eutrophication is defined as the process by which a body of water becomes enriched in dissolved nutrients (nitrates, phosphates and ammonium ions) that stimulate the growth of aquatic plant life, e.g. algae blooms, usually resulting in the depletion of dissolved oxygen. In order to minimize these detrimental effects, government regulations often limit the concentrations of nitrogen (ammonium ions and nitrates) and phosphorus (phosphates).
There are several advantages to removing ammonium ions from waste water. Reuse of municipal waste water requires a 90-95% reduction in the ammonium ion concentration typically found in waste water. In the past this treatment has been prohibitively costly. Chlorine disinfection of water is also affected since ammonium ions react with chlorine to form chloramines which, while still bactericides are slower acting and less effective. Finally, ammonium cations are corrosive to certain metals and other materials.
Some municipal wastewater treatment plants have used the zeolite clinoptilolite to remove ammonium ions from wastewater. J. D. Sherman and R. I. Ross in xe2x80x9cProceedings of the Fifth International Conference on Zeolitesxe2x80x9d, L. V. C. Rxc3xa9es, editor, Heyden Press, pp. 823-831 (1980), disclose the use of zeolites F and W for removing ammonium ions from a synthetic wastewater. In U.S. Pat. No. 4,344,851 B1 it is disclosed that phillipsite type zeolites can remove ammonium ions in the presence of calcium ions.
In contrast to these zeolites, applicants have developed a composite which contains an anion and a cation exchanger. The cation exchanger is a microporous composition having an empirical formula on an anhydrous basis of:
ApMxZr1-xSinGeyOmxe2x80x83xe2x80x83(I)
or
ApMxTi1-xSinGeyOmxe2x80x83xe2x80x83(II)
where A is an exchangeable cation selected from the group consisting of potassium ion, sodium ion, rubidium ion, cesium ion, calcium ion, magnesium ion, hydronium ion or mixtures thereof, M is at least one framework metal selected from the group consisting of hafnium (4+), tin, (4+), niobium (5+), titanium (4+), cerium (4+), germanium (4+), praseodymium (4+), and terbium (4+), except that M is not titanium in formula (II), xe2x80x9cpxe2x80x9d has a value from about 1 to about 20, xe2x80x9cxxe2x80x9d has a value from zero to less than 1, xe2x80x9cnxe2x80x9d has a value from 0 to about 12, xe2x80x9cyxe2x80x9d has a value from 0 to about 12, xe2x80x9cmxe2x80x9d has a value from about 3 to about 36 and 1xe2x89xa6n+yxe2x89xa612. The germanium can substitute for the silicon, zirconium/titanium or combinations thereof. Examples of the anionic exchange composition are hydrous zirconium oxide and zirconia.
This invention relates to a process for removing pollutants from aqueous streams. Accordingly, one embodiment of the invention involves contacting the aqueous stream with a shaped ion exchange composite at ion exchange conditions thereby removing at least some of the pollutants, the composite comprising a mixture of a microporous cation exchange composition and an anion exchange composition, where the cation exchange composition is selected from the group consisting of zirconium metallate, titanium metallate and mixtures thereof, the metallates respectively having an empirical formula on an anhydrous basis of:
ApMxZr1-xSinGeyOmxe2x80x83xe2x80x83(I)
or
ApMxTi1-xSinGeyOmxe2x80x83xe2x80x83(II)
where A is an exchangeable cation selected from the group consisting of potassium ion, sodium ion, calcium ion, magnesium ion and mixtures thereof, M is at least one framework metal selected from the group consisting of hafnium (4+), tin (4+), niobium (5+), titanium (4+), cerium (4+), germanium (4+), praseodymium (4+), and terbium (4+), except that M is not titanium in formula (II), xe2x80x9cpxe2x80x9d has a value from about 1 to about 20, xe2x80x9cxxe2x80x9d has a value from zero to less than 1, xe2x80x9cnxe2x80x9d has a value from 0 to about 12, xe2x80x9cyxe2x80x9d has a value from 0 to about 12, xe2x80x9cmxe2x80x9d has a value from about 3 to about 36 and 1xe2x89xa6n+y xe2x89xa612, and the anion exchange composition is selected from the group consisting of hydrous zirconium oxide, zirconia, alumina, titania, hydrous titanium oxide, layered double hydroxides, single phase metal oxide solid solutions, magnesium hydroxide, calcium hydroxide, silica, amorphous mixed metal oxides, basic clays and mixtures thereof.